The free world is the new continent in cyberspace that we have built so we can live here in freedom. It's impossible to live in freedom in the old world of cyberspace, where every program has its feudal lord that bullies and mistreats the users. So, to live in freedom we have to build a new continent. Because this is a virtual continent, it has room for everyone, and there are no immigration restrictions. - Richard Stallman -

Systemd is a system and service manager for Linux, compatible with SysV and LSB init scripts. systemd provides aggressive parallelization capabilities, uses socket and D-Bus activation for starting services, offers on-demand starting of daemons, keeps track of processes using Linux cgroups, supports snapshotting and restoring of the system state, maintains mount and automount points and implements an elaborate transactional dependency-based service control logic. It can work as a drop-in replacement for sysvinit. For more information, watch the video at http://www.youtube.com/watch?v=TyMLi8QF6sw

For system administrators.System administrators can visit this page, to understand how to use the native systemctl calls that replace their old workflow in SysVinit. Note that the service and chkconfig commands will continue to work as expected in the systemd world.

Tools.

systemctl: used to introspect and control the state of the systemd system and service manager

systemd-cgls: recursively shows the contents of the selected Linux control group hierarchy in a tree

systemadm: a graphical frontend for the systemd system and service manager that allows introspection and control of systemd. Part of the systemd-gtk package. This is an early version and needs more work. Do not use it for now unless you are a developer.

View the man pages for more details.

Boot Kernel Command Line.

On boot systemd activates (by default), the target unit default.target whose job is to activate services and other units by pulling them in via dependencies.

To override the unit to activate, systemd parses its own kernel command line arguments via the systemd.unit= command line option. This may be used to temporarily boot into a different boot unit. The classical run-levels are replaced as following:

systemd.unit=rescue.target is a special target unit for setting up the base system and a rescue shell (similar to run level 1); systemd.unit=emergency.target, is very similar to passing init=/bin/sh but with the option to boot the full system from there; systemd.unit=multi-user.target for setting up a non-graphical multi-user system; systemd.unit=graphical.target for setting up a graphical login screen.

For details about these special systemd boot units, view the man systemd.special page. it scripts

What is the tool to manage services with systemd?

systemctl is the primary tool to use. It combines the functionality of both service and chkconfig into a single tool that you can use for instance to enable/disable services permanently or only for the current session.

list all running services etc:

systemctl

Refer to man systemctl for more details. systemd-cgls lists the running process in a tree format. It can recursively show the content of any given control group. Refer to man systemd-cgls for more details.

How do I start/stop or enable/disable services?

Activates a service immediately:

systemctl start foo

Deactivates a service immediately:

systemctl stop foo

Restarts a service:

systemctl restart foo

Shows status of a service including whether it is running or not:

systemctl status foo

Enables a service to be started on bootup:

systemctl enable foo

Disables a service to not start during bootup:

systemctl disable foo

Prevent a service from starting dynamically or even manually unless unmasked:

systemctl mask foo

Check whether a service is already enabled or not:

systemctl is-enabled foo

Refer to man systemctl for more details.

How do I change the target (runlevel)?

systemd has the concept of targets which is a more flexible replacement for runlevels in sysvinit.

Run level 3 is emulated by multi-user.target. Run level 5 is emulated by graphical.target. runlevel3.target is a symbolic link to multi-user.target and runlevel5.target is a symbolic link to graphical.target.

You can switch to 'runlevel 3' by running

systemctl isolate multi-user.target

You can switch to 'runlevel 5' by running

systemctl isolate graphical.target

How do I change the default target?

systemctl set-default <name of target>.target

graphical.target is the default. You might want multi-user.target for the equivalent of non graphical (runlevel 3) from sysv init. The full list of targets can be accessed via systemctl list-units --type=target

systemd does not use /etc/inittab file.

How do I know the current target?

systemctl get-default

How to power off the machine ?

You can use

poweroff

Some more possibilities are: halt -p, init 0, shutdown -P now

Note that halt used to work the same as poweroff in previous Fedora releases, but systemd distinguishes between the two, so halt without parameters now does exactly what it says - it merely stops the system without turning it off.

Does service command work with systemd?

Yes. It has been modified to call systemctl automatically when dealing with systemd service files. So either of the following commands does the same thing

systemctl stop NetworkManager

(or)

service NetworkManager stop

Does chkconfig command work with systemd?

Yes, for turning on/off services, compatibility has been provided both ways. chkconfig has been modified to call systemctl when dealing with systemd service files. Also systemctl automatically calls chkconfig when dealing with a traditional sysv init file.

Note that if you exit tty8 session, you wont be able to use it until next reboot or manual start by systemctl, except if you leave Restart as ‘always’, but I highly recommend to avoid this according to security reasons.

How do I customize a unit file/ add a custom unit file?

The best way to customize unit files is to add /etc/systemd/system/foobar.service.d/*.conf where foobar.service is the name of the service you want to customize. If a directory doesn't already exist, create one and drop a conf file with the settings you want to override. For example,

Don't forget to reload systemd daemon using systemctl daemon-reload and systemctl restart foobar after editing a unit file where foobar is the name of the unit. Also note that you can systemd-delta to list the unit files which have been customized and also the precise differences

Special care must be taken when overriding options which can be set muliple times (ExecStart, ExecStartPre, ExecStartPost are a common example). Assigning some value to the option appends to the existing list, while assiging the empty value resets the list.

The same rules apply to snippets in .d directories. This means that snippets which override ExecStart and similar settings, often should start with the empty assignment ExecStart=, followed by the new setting.

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